problem with wide plank flooring

I installed about 800 square feet of 9" wide white pine flooring this past summer, and I am experiencing what I believe to be excessive shrinkage. Some of the planks have shrunk so bad that the tongue is no longer in the groove! I had installed 100 square feet in one of the bedrooms three years ago and there was hardly any shrinkage in that room at all. I am looking for any potential solutions to get the flooring to expand back to the original width or at least somewhat close. Any and all advice would be most appreciated.

I thought this would be a

I thought this would be a good place to ask this question, a lot of east coasters on this site! Wide plank, especially white pine is not a common choice here in the midwest, I know it is more popular out east.

Moisture content (MC) is very

Moisture content (MC) is very critical. The plank flooring should ideally be stickered in the rooms they will be installed in until the MC is equivalent to the existing subfloor. Ideally wood flooring should be installed during spring or fall when ambient humidity levels are lowest. Also a slip sheet such as red rosin paper or ideally 15# felt paper (which is also a vapor barrier) should be laid down between the subfloor and finished flooring. The basement or crawl space should also be dry and possibly dehumidified during the summer if necessary. And finally you might also add humidification (relatively easy if you have a forced air heating system) in the dry winter months to keep the floor from contracting. I have applied all of the above in the past and have had very little movement with wide plank pine flooring in the notheast with very extreme temperature and humidity swings. Good luck.

The floor is on 3/4" 1x8

The floor is on 3/4" 1x8 which I screwed and made sure it was tight, 2x8 joists, 24' on center. This house was built around 1922 so I went with what was there. Not sure of the moisture content, maybe thats where I made my mistake. Basement is dry, one small section is a crawl but it is dry also. I will check the humidity.